The present invention relates to a closed cycle refrigeration system utilizing a remote condenser and constructed so as to improve the efficiency of operation of the system and reduce the power consumption.
In the basic construction of any closed cycle refrigeration system, the gaseous refrigerant, e.g. freon, is compressed within a compressor so as to be present as a high temperature compressed gas. The compressed gas is then condensed within a condenser into a liquid. The pressure within the condenser is maintained at an appropriate level so that the gaseous refrigerant will be transformed into a liquid at a temperature level higher than the ambient air. Thus, as the gaseous refrigerant passes through the condenser, it can give off heat to the surrounding ambient air. The liquid refrigerant emitted from the condenser is then temporarily stored in a receiver and subsequently passed through an evaporator within a display case. As the liquid passes through the evaporator, it extracts heat from the display case and is converted back into its high temperature gaseous state. This gaseous refrigerant is then again passed through the compressor and the cycle is continued.
Traditionally, the condenser was operated at a preselected design temperature level. Thus, once it was determined what the highest ambient temperature was during a normal period of the warmest season in a particular area, the design temperature for the condenser was set at this level. Then, the condenser was operated so as to condense the gaseous refrigerant at a temperature of at least 10.degree. F. above this design temperature. Consequently, if the design temperature was 90.degree. F., then the condenser temperature was set at 100.degree. F.
Recognizing that the design temperature was only likely to occur a few days in a year, and then only during the day and not at night, the refrigeration systems have been modified so that the condenser temperature followed the path of the ambient temperature while always remaining at least 10.degree. F. above the ambient temperature.
During the operation of the refrigeration system, it is necessary to regulate the pressure within the receiver in order to ensure proper operation of the evaporators. Such regulation has typically been provided by shunting hot gaseous refrigerant from the gas discharge line of the compressor directly into the receiver whenever the relative pressure of the receiver drops by more than a preselected pressure differential from the pressure in the gas discharge conduit. For such purposes, a check valve, typically on the order of 20 or 30 psi, has been provided in the line between the gas discharge conduit and the receiver. Hence whenever the pressure within the receiver drops by more than 20 or 30 psi as compared to the pressure in the gas discharge conduit the check valve opens and allows the hot gas from the gas discharge line to flow directly into the receiver. Since the gaseous refrigerant in the gas discharge conduit is typically of a temperature level of aproximately 200.degree. F., such gas acts as a significant heat source to the receiver, a situation which is generally undesirable.
During the refrigeration cycle, the refrigerant absorbs a substantial amount of heat during the evaporation stage, which heat is then dissipated by the condenser as a waste by-product of the refrigeration cycle. In certain refrigeration systems, effective use of such heat has been made by employing a gas defrost operation. Such a gas defrost operation utilizes a certain amount of this extra heat by periodically channeling some of the hot compressed gaseous refrigerant back to the evaporator where this heat is then given up by the gaseous refrigerant to defrost the evaporator. Such a system is disclosed in U.S. patent application, Ser. No. 952,612 to Arthur Perez and Fayez Abraham, filed on Oct. 10, 1978, now U.S. Pat. No. 4,276,755, which application is assigned to the same assignee as the present application. The contents of such application is hereby incorporated by reference.
In one type of conventional gas defrost system, super-heated gaseous refrigerant is periodically channeled directly from the compressor output into one or more selected evaporator coils for melting the frost accumulated on the coils. Examples of such systems are shown in U.S. Pat. No. 3,138,007 to Friedman, et al. and U.S. Pat. No. 3,150,498 to Blake. Other conventional gas defrost systems remove the super abundance of sensible heat from the compressor discharge gas so that the defrost gas conveyed to a selected evaporator to be defrosted is at or close to the saturation temperature of the refrigerant. Examples of such systems are shown in U.S. Pat. No. 2,895,306 to Latter and U.S. Pat. No. 3,343,375 to Quick. Still, other prior art systems remove both super heat and latent heat from the defrosting refrigerant so that only condensed liquid refrigerant is conveyed to the evaporator to be defrosted such as disclosed in U.S. Pat. No. 3,195,321 to Decker, et al. Another type of system increases the heat content of the defrost gas by means of external electric heaters and the like such as disclosed in U.S. Pat. No. 3,145,602 to Beckwith.
During the operation of such gas defrost systems, the refrigeration cycle is temporarily deactivated and hot gases are then fed through the evaporator coils for defrosting such coils. After the evaporator coils have been sufficiently defrosted, the flow of the gaseous refrigerant is cut off and the evaporator coils are immediately returned to a refrigeration cycle of operation.
Another technique for taking advantage of the heat to be dissipated by the hot gaseous refrigerant is the utilization of a heat recovery coil such as shown in U.S. Pat. No. 4,123,914 to Arthur Perez and Edward Bowman, which patent is assigned to the same assignee as the present application and is hereby incorporated by reference. Such a heat recovery coil allows for extraction of heat from the gaseous refrigerant flowing out of the compressor before entering the remote condenser. Such extracted heat then can be utilized for heating the interior of the building where the refrigeration system is employed. Similar types of systems are disclosed in U.S. Pat. No. 3,905,202 to Taft, et al. and No. 4,012,921 to Willitts, et al. These last two patents also disclose the utilization of gas defrost mechanisms within the refrigeration systems.
In the utilization of such refrigeration systems, significant attention has been given, especially in recent years, to improving the power efficiency of the systems. The previously noted patents to Perez, et al. U.S. Pat. No. (4,123,914), Taft, et al. and Willitts, et al. all discuss various different techniques for attempting to improve the operation of a refrigeration system. In large installations, such as supermarkets, there are typically large number of refrigerated display cases and hence, typically a plurality of compressors are employed in order to satisfy the heavy refrigeration load under certain conditions, such as during the warmer portions of the year. The efficiency of the compressors is dependent upon the compression ratio of the discharge side of the compressor to the suction side of the compressor. Thus, by reducing the head pressure at the compressor discharge, the efficiency of operation of the compressor can be increased.